1. Field of the Invention
The present invention relates to a toner for non-magnetic one-component developer, a method of preparing the toner, and a developer and an image forming method using the toner.
2. Discussion of the Background
Conventionally, heat roll methods are widely used for fixing a toner. A toner image contacts the surface of the heat roll with pressure in the state of being melted upon application of heat. Therefore, preventing a phenomenon (hot offset phenomenon) in which the toner image partially adheres to the surface of the heat roll and contaminates a following medium a toner image is fixed on. In addition, a separator such as a separation click or an oil applicator is formed on the roll to prevent the medium such as a paper from winding around the roll when passing the roll. However, recent copiers or printers being downsized mostly use oilless fixing methods without the oil applicator, and in which the conventional heat roll methods cause a separation failure unless the fixer and the toner are tailored.
Methods of including a large amount of a wax such as polypropylene and polyethylene in a toner to improve the releasability thereof melted with heat, and methods of coating the surface of the heat roll with a resin having good separativeness such as a fluorochemical resin are disclosed. However, the wax such as polypropylene and polyethylene has low compatibility with a polyester resin having a high polarity, which is used for preparing a toner, and is difficult to fill therein in a large amount. In order to solve this problem, a method of using a modified wax such as an oxidized polyolefin wax having a polar group at its molecular end to improve the compatibility of the wax with the polyester resin and increase the dispersibility and a mount thereof filled in a toner. However, the modified wax has a higher viscosity than an unmodified wax although having improved dispersibility and a dispersion diameter thereof is so small that the releasability thereof deteriorates, resulting in occurrence of hot offset phenomenon.
Particularly, color toners noticeably have the hot offset and separativeness problems. Namely, the color toner needs to have higher melting performance with heat and lower viscosity than a black toner to have gloss, transparency and color reproducibility. However, a color toner including a resin satisfying such requirements possibly deteriorates in intermolecular cohesion when melted with heat and adheres to the heat roll more when passing the heat roll, resulting in noticeable occurrence of the separation failure and hot offset. In order to prevent the separation failure and hot offset, a wax is filled in a toner in a large amount to reduce adherence of the toner to the heat roll. However, a large amount of the wax causes a larger dispersion diameter thereof and free waxes increase, resulting in image noise.
Recently, the dispersion diameter of a wax in a toner is specified to solve the above-mentioned problems.
Japanese Patent No. 3458629 discloses a nonmagnetic toner for forming a full-color image containing at least a resin binder, a colorant and wax particles having a particle size distribution in which wax particles having not less than 3 μm not 3% or less by number, wax particles having 2 to less than 3 μm for 12% or less by number, wax particles having 1 to less than 2 μm 5 to 30% by number and wax particles having less than 1 μm 55 to 95% by number. Japanese Published Unexamined Patent Application No. 2004-126268 discloses a toner composition consists essentially of a binder resin, two waxes incompatible with the binder resin and a colorant, and in the number-particle size distribution of dispersion particle diameter of each wax, the standard deviation is not less than 0.4 and less than 2.0, the top peak is present between 1.0 and 1.5 μm, the number proportion of wax particles of not less than 1.0 and less than 1.5 μm is not less than and less than 40%, and the number proportion of wax particles of not less than 2.5 μm is less than 20%. However, the toner of Japanese Patent No. 3458629 includes the wax having a very small dispersion diameter and does not have satisfactory separativeness in oilless fixing. The toner of Japanese Published Unexamined Patent Application No. 2004-126268 including two waxes is likely to have a broad dispersion diameter distribution of the wax and difficult to have a sharp dispersion diameter distribution thereof. Therefore, a toner needs to be filled with a large amount of the wax to have good separativeness and is very difficult to have both thermostable storage stability and a prohibitive power of free wax.
Because of these reasons, a need exists for a toner for a non-magnetic one-component developer, having good separativeness, a prohibitive power of free wax and thermostable storage stability.